With 5.5 score in IELTS, joining a MBA program is quite difficult. Some universities offer admission for students with 5.5 score in IELTS but you may be asked to join ESL (English as a Second Language) program. Rather than looking for admission with 5.5 IELTS score, you better retake IELTS and score at least 7.0 for admission at good business schools. However, if you want to join MBA program with 5.5 score, here are some business schools which may accept you:

Southern New Hampshire University
University of Missouri
The University of Scranton